- Title
- Beam focal spot position: the forgotten linac QA parameter. An EPID-based phantomless method for routine Stereotactic linac QA
- Creator
- Chojnowski, Jacek M.; Barnes, Michael P.; Sykes, Jonathan R.; Thwaites, David I.
- Relation
- Journal of Applied Clinical Medical Physics Vol. 18, Issue 5, p. 178-183
- Publisher Link
- http://dx.doi.org/10.1002/acm2.12147
- Publisher
- John Wiley & Sons
- Resource Type
- journal article
- Date
- 2017
- Description
- Modern day Stereotactic treatments require high geometric accuracy of the delivered treatment. To achieve the required accuracy the IGRT imaging isocenter needs to closely coincide with the treatment beam isocenter. An influence on this isocenter coincidence and on the spatial positioning of the beam itself is the alignment of the treatment beam focal spot with collimator rotation axis. The positioning of the focal spot is dependent on the linac beam steering and on the stability of the monitor chamber and beam steering servo system. As such, there is the potential for focal spot misalignment and this should be checked on a regular basis. Traditional methods for measuring focal spot position are either indirect, inaccurate, or time consuming and hence impractical for routine use. In this study a novel, phantomless method has been developed using the EPID (Electronic Portal Imaging Device) that utilizes the different heights of the MLC and jaws. The method has been performed on four linear accelerators and benchmarked against an alternate ion chamber-based method. The method has been found to be reproducible to within ±0.012 mm (1 SD) and in agreement with the ion chamber-based method to within 0.001 ± 0.015 mm (1 SD). The method could easily be incorporated into a departmental routine linac QA (Quality Assurance) program.
- Subject
- EPID; focal spot; quality assurance; medical linear accelerators
- Identifier
- http://hdl.handle.net/1959.13/1396875
- Identifier
- uon:34143
- Identifier
- ISSN:1526-9914
- Rights
- © 2017 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
- Language
- eng
- Full Text
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